The blooms, which occur when cyanobacteria overgrows in a water body, can cause gastrointestinal upset and allergic reactions, among other symptoms, in people and animals, according to the county health department.

The county advised people to stay away from the affected waters and to keep their pets and children away from the areas.

A Jack Russell terrier died in 2012 after drinking water from Georgica Pond in East Hampton during a bloom.

Last month, a bloom was found in Marratooka Lake in Mattituck, but that water body has since been removed from the DEC's list of active algal blooms.